Field of the Invention
The present invention relates to an image forming apparatus such as a copier or a printer which has a function to form an image on a recording material, and an image forming method.
Description of the Related Art
Image forming apparatuses such as electrophotograhic copiers and printers generally form images on recording materials in the process described below. First, a photosensitive member is scanned by light from a laser scanner to form an electronic latent image on the member, which is then developed using toner to form a toner image. The toner image is transferred to a recording material directly from the photosensitive member or via an image bearing member, such as an intermediate transfer member. Then, the recording material with the toner image transferred thereto is heated and pressed by a fixing apparatus to form an image on the recording material. Here, some fixing apparatuses may include a fixing roller or film that is heated by a heat source and a pressure roller that comes into contact with the fixing roller or film to form a fixing nip.
Fixing conditions for the fixing apparatus are generally set such that the image can be fixed even if the maximum amount of toner that can be allowed for the image forming apparatus is loaded on the recording material, and the fixing conditions may not be changed even with a smaller amount of toner. For example, in a color image forming apparatus, even a text image will be fixed at a fixing temperature at which even a solid image in whole area of the recording material can be fixed. As a result, the image with a small amount of toner is fixed at an excessive temperature. This leads to excessive fixture and may disadvantageously result in hot offset, curling of the recording material, or consumption of more power than is necessary.
To solve these problems, Japanese Patent Application Laid-Open No. 2006-154413 discloses an image forming apparatus using toner in a plurality of colors, which is configured to detect overlap of dots when an image is formed using the dots and to change the fixation setting condition according to the number of overlaps. Furthermore, Japanese Patent Application Laid-Open No. 2009-92688 discloses an image forming apparatus also using toner in a plurality of colors, which is configured to detect overlap of toner colors in one dot line and to change the fixing condition according to the state of the overlap.
However, with the increased resolution and operating speed of recent image forming apparatuses, there is a need for an image forming apparatus which can quickly acquire density information from image data so as to reflect the density information in the fixing condition before a fixing process is started.